1. Field of the Invention
This invention relates to pressurized heat exchangers and more specifically to an arrangement for relieving excessive pressure differentials within the heat exchanger in the event of a failure in the secondary coolant supply system.
2. Description of the Prior Art
The use of heat exchangers in conjunction with pressurized water reactors is well known. Typically, the heat exchanger takes the form of a vertically oriented elongated cylindrical pressure vessel containing a plurality of closely spaced tubes extending throughout the entire length of the vessel forming a tube bundle.
At both ends of the tube bundle a horizontally transposed tubesheet holds the tubes in position. A cylindrical tube shroud surrounds the tube bundle, and cooperates with the vessel wall to form an annular passage therebetween. A horizontally oriented partition wall circumscribes the tube shroud and divides the annular space into a fluid inlet compartment and fluid outlet compartment.
In this particular arrangement, a hot primary coolant enters the pressure vessel through an inlet nozzle, located at the base of the vessel, travels up through the tubes housed within the vessel, and exits through an outlet nozzle located at the head of the vessel. Simultaneously, secondary feedwater enters through a feedwater inlet nozzle, passes through the inlet compartment and is vaporized as it travels upwardly and around the tubes, and is then redirected downwardly through the fluid outlet compartment for discharge through the steam outlet nozzle.
During normal operating conditions, the shell side pressure may be in the order of 1085 psi. However, if either the secondary feedwater line or the main steam line should rupture, the pressure will quickly drop in the compartment connected with the ruptured line causing a large pressure differential across the two compartments. Such a pressure drop may cause extensive damage to the internal components of the vessel.
It is obvious that a reliable pressure equalization mechanism is therefore necessary to relieve the resulting pressure differential between the two compartments before serious damage occurs.